The present invention relates to tires and particularly to aspects of the design of the tread region of the tire which can facilitate the dispersal of trapped air in the molding and vulcanizing operation of the tire manufacturing process.
A problem which commonly arises in the molding of elastomeric articles such as tires is the trapping of air between the surfaces of the article and the mould. Such trapped air prevents the elastomeric article from contacting the mould surface and thus locally reduces conductive heat transfer which effects vulcanization in an uncontrolled way and spoils the finished surface appearance. In the tire art such resultant blemishes are termed xe2x80x9cbarenessxe2x80x9d.
In tires having block-type tread patterns, bareness on the top surface of the blocks can be a particular problem due to their relatively flat surface.
To help prevent bareness on tires, tire moulds are commonly vented by means of holes of very small diameter provided through the mould wall. Such vent holes allow trapped air to escape but suffer the disadvantage that rubber can also flow into the hole resulting in bristle-like projections or xe2x80x98spue-pipsxe2x80x99 covering the surface of the molded tire.
Such spue-pips detract from the visual appearance of the tire and are normally removed by rotating the tire against a trimming knife held to the tire surface. However such removal of spue-pips in the tire tread region presents a particular problem because of the potential damage which can be done to the salient features of the tread pattern.
Accordingly it is an object of the present invention to provide a tire in which features of the tread pattern can assist in dispersal of trapped air in molding, thereby reducing the need for vent holes in the tread region.
According to the present invention there is provided a tire having a ground contacting tread comprising tread grooves dividing the tread into a plurality of pattern elements each having edges, wherein at least one pattern element is provided on its radially outer surface with a radially outwardly projecting ridge disposed on an edge of the pattern element and at least one radially inwardly projecting small groove which extends to the projecting edge.
By small groove is meant a groove having a width and depth not more than 3 mm.
Preferably a plurality of small grooves are provided.
The combination of small grooves in the surface of a tread pattern element which communicate with a raised ridge on the edge of the element has proven effective in dispersing, during molding, trapped air from the tread region without the need for venting.
Preferably the surface of the pattern element is criss-crossed by a plurality of such intersecting small grooves.
Sipes or knife-cuts may also be provided in the pattern element and may also be wholly contained within one or more of the small grooves.